Re: [boost] [system] Add noexcept to conform with C++11

Subject: Re: [boost] [system] Add noexcept to conform with C++11
From: Beman Dawes (bdawes_at_[hidden])
Date: 2012-12-09 09:03:24

On Sun, Dec 9, 2012 at 5:00 AM, Vicente J. Botet Escriba
<vicente.botet_at_[hidden]> wrote:
> Le 08/12/12 21:19, Beman Dawes a écrit :
>
>> On Sat, Dec 8, 2012 at 8:42 AM, Vicente J. Botet Escriba
>> <vicente.botet_at_[hidden]> wrote:
>>>
>>> Hi,
>>>
>>> any news on https://svn.boost.org/trac/boost/ticket/7278.
>>>
>>> I could add them if you don't have the time now.
>>
>> Go ahead!
>>
>>
> As the change is a breaking change I would like to update all the libraries
> at once. I have identified the following dependent libraries: asio,
> filesystem, thread. Are there other libraries?

chrono?

We need to contact Chris Kohlhoff to coordinate any asio changes with
him. I have a vague recollection that he maintains the asio codebase
elsewhere, so boost trunk is really just a mirror of some other repo.
But I could be wrong about that.

>
> Should I introduce the change conditionally so that the users could comeback
> to the preceding semantics?
>
> I was thinking on defining a new BOOST_SYSTEM_NOEXCEPT that the users will
> use instead of BOOST_NOEXCEPT. The user could define BOOST_SYSTEM_NOEXCEPT
> as nothing to get the old semantic.
> Of course as the needed change in the user code is minor, we could also
> choose the drastic way and add a breaking change respect to the preceding
> version.

What happens if a user has built boost libraries without defining
BOOST_SYSTEM_NOEXCEPT but then compiles his or her own code with
BOOST_SYSTEM_NOEXCEPT defined, or visa versa? Isn't that an ODR
violation? Could this result in the generated code for a call to a
boost.system function being incompatible with the code that was
generated when the library was built? And wouldn't such a bug be
particularly insidious because it  might not cause a problem until
some future date when an error occurred?

That seems a lot worse than the noisy compiler error that will happen
if user code just broke. How many folks are using a compiler that
supports C++11 noexcept, have C++11 turned on, and are deriving from
boost::system_error? Or am I missing other cases where user code would
break?

> Beman up to you to decide.

I want to hear from others, particularly Chris, before making a decision.

--Beman